The present invention relates to apparatus for ascertaining and monitoring the accumulations of flowable solid material in containers for flowable material, particularly in the hoppers of dust separators in large chemical or other plants.
Dust separators (such as electrostatic precipitators, bag filters, bag houses and the like) are used in flue gas systems of power stations and are normally operated at a reduced pressure under the action of an induced draft fan serving to draw flue gases and/or other gases which are to be relieved of dust and/or other flowable solid material through one or more dust separators and into a stack or another exhaust system. Solid material which is separated from flue gases normally descends into one or more hoppers or analogous containers preferably having conical, funnel-shaped or similar bases leading to discharge openings for evacuation of accumulated solid material. It happens again and again, particularly as a result of bridging, compacting, agglomeration or a combination of such undesirable phenomena, that the solid material blocks the discharge opening or openings of one or more hoppers and begins to rise. While it is customary to tolerate certain accumulations of dust and other flowable solid materials, corrective measures must be undertaken when the accumulated solid material piles up to a predetermined level. This is the reason for the provision of apparatus which monitor the level of the accumulated solid material in the hoppers and are designed to generate warning signals as soon as the accumulated material in a hopper reaches a predetermined level.
In a large power station, the hoppers of dust precipitators are often installed at a considerable distance (e.g., many meters) above the ground level, and the predetermined level to which the accumulate solid material is permitted to rise in a hopper before the monitoring apparatus generates a signal is well above (normally many meters above) the level of the discharge openings at the bottom ends of the hoppers. Certain presently known level sensing apparatus employ electrically energized tuning forks which are installed in the hoppers at predetermined levels above the discharge openings and cease to vibrate as soon as they become embedded in a pile of accumulated solid material. This gives rise to the generation of a signal by suitable electronic monitoring means. A drawback of such level sensing apparatus is that a tuning fork is prone to malfunction as a result of corrosion and/or accumulation of dust thereon and, consequently, it must be accessible for inspection, cleaning or replacement. It is further known to employ other electronic level sensing apparatus, e.g., apparatus employing capacitance-responsive sensors which are mounted in the hoppers and, consequently, are prone to malfunction on the aforediscussed grounds and/or for other reasons. It is also known to employ pressure-responsive sensors which are installed in the walls of the hoppers above the predetermined level of permissible accumulation of solid material and comprise open-ended pipes extending downwardly into the respective hoppers to the predetermined level. Such pressure-sensitive sensors also require frequent cleaning and other forms of maintenance. This is possible only by affording access to the level sensing apparatus, e.g., by providing expensive and often dangerous staircases, service platforms and/or other facilities in order to enable the person in charge to reach and service the apparatus. The just outlined problems have existed for many decades and the presently known solutions are far from ideal or even halfway satisfactory.